The present invention relates to a bearing assembly incorporating a mechanism for detecting the number of the rotation of wheels of an automobile. More particularly, the invention relates to a bearing assembly capable of preventing erroneous detection of the number of the rotation of shafts and wheels of an automobile from occurrence conventionally being caused by rust.
The number of the rotation of an automobile is detected by operating an anti-skid brake system (ABS) mounted thereon. As shown in FIG. 3 for example, the Japanese Laid-Open Patent Publication No. HEI2-299902 of 1990 discloses such a device for detecting the number of the rotation of wheels of an automobile. This prior art provides a bearing assembly comprising; an external wheel hub 31 substantially being an external member which forms a specific pulser portion 32 on its external circumferential surface for rotating itself in conjunction with wheels and a raceway surface 33 on its internal circumferential surface; an internal wheel 41 substantially being an internal member which forms the other raceway surface 42 on external circumferential surface and accommodates a stationary shaft (not shown) inserted in an internal circumferential surface 43; and a plurality of balls respectively being disposed between raceway surfaces of the external and internal wheels. The pulser portion 32 composed of multiple projections protruding radially at a constant internal in the circumferential direction is formed as an external gear to the external circumferential surface of the external wheel hub 31. In association with the bearing assembly cited above, a pickup sensor 51 is disposed in opposition from the pulser portion 32 across predetermined clearance.
There are a variety of proposals on the pickup sensor 51 disposed in opposition from the pulser portion 32 provided for the external wheel 31. Basically, the pickup sensor 51 incorporates a magnetic circuit in order to detect variation of flux density of the pulser portion 32 incidental to the rotation of the wheels as precisely as possible.
In the event that rust is generated on the external wheel hub 31 making up a device for detecting:the number of the rotation of wheels, in many cases, troublesome situation occurs without being able to disengage wheels from the chassis. In particular, the pulser portion 32 formed to the external wheel hub 31 is more gravely affected by rust than the external wheel hub 31, thus resulting in occurrence of significant error in the detected number of pulses. Nevertheless, when integrally forming the pulser portion 32 in association with the external wheel hub 31, extreme difficulty prevents the above-cited prior art from properly effecting rust-proof finishing. More particularly, execution of rust-proof thermal treatment at a high temperature often results in the tempering of the quenched raceway track, and in addition, when the rust-proof quenching process is executed before quenching the raceway track, because of quenched effect given to the raceway track, rust-proof effect is easily dissipated.